Method of regulating an internal combustion engine

ABSTRACT

Method of regulating an internal combustion engine in order to reach presettable nitrogen oxide emission values of the internal combustion engine, wherein the internal combustion engine is supplied at least some of the time with a first fuel and at least some of the time with a second fuel, the quantity of the first fuel supplied to the internal combustion engine per unit of time being controlled according to a preset control actual value or kept constant and the quantity of the second fuel supplied to the internal combustion engine per unit of time to reach a presettable nitrogen oxide emission value being regulated according to at least one recorded engine parameter.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Austrian Application No. A 888/2004,filed May 21, 2004, the contents of which are incorporated by referencein their entirety.

BACKGROUND OF THE INVENTION

The present invention relates to a method of regulating an internalcombustion engine, in particular with a lean operating mode, in order toreach presettable nitrogen oxide emission values of the internalcombustion engine. The invention also relates to a correspondingregulator and internal combustion engine.

It is already known from EP 0 259 382 B1 to operate an internalcombustion engine for driving an electric generator with constantnitrogen oxide emission values, by regulating the mixture pressurebefore the inlet valves of the cylinders according to the electricoutput delivered by the generator. The target value of the mixturepressure in the intake before the inlet valves is taken from acharacteristics field which shows the dependency of the mixture pressureon the delivered electric output with constant emission values. Themeasured actual value of the pressure before the inlet valves is thenregulated, via an adjustment of the fuel-to-air ratio in a gas mixer, toits target value determined via the characteristics field. Thecharacteristics field used for this is produced by gauging at least twooperating points with identical NO_(x) emission values. It is possible,through this previously known method, that an internal combustion enginecan very precisely observe the desired emission values in a wide outputrange. The system known from the named European patent has the advantagethat there is practically no wear and ageing of sensitive sensors.

A further improved system according to the preamble is presented in theEuropean patent application EP 1 225 330 A2, in which the regulationscheme known from EP 0 259 382 B1 has been supplemented by an ignitionpoint adjustment in order to provide, in every operating condition, aregulation reserve for rapid reaction to load changes. This regulationalso serves to always run the internal combustion engine with an optimumdegree of efficiency.

Each of the previous regulation methods is designed only for operationwith one fuel type. However, there are also internal combustionengines—principally stationary—which are operated with two differentfuel types. No regulation method with which the reaching of presettablenitrogen oxide emission values is assured is known to date for suchengines.

SUMMARY OF THE INVENTION

The object of the present invention is therefore to create such aregulation method for internal combustion engines.

This is achieved according to the invention by supplying the internalcombustion engine at least some of the time with a first fuel and atleast some of the time with a second fuel, the quantity of the firstfuel supplied to the internal combustion engine per unit of time beingcontrolled either according to a control target value preset or keptconstant, and the quantity of the second fuel supplied to the internalcombustion engine per unit of time being regulated according to at leastone recorded engine parameter in order to reach the presettable nitrogenoxide emission value.

An idea underlying the present invention is thus, in the case ofinternal combustion engines which are operated at least some of thetime, with two different fuel types, to control in an open-loop mode thevolume flow (=quantity supplied to the internal combustion engine perunit of time) of the one first fuel according to fixed preset values orto keep it constant. During this time, the internal combustion engine isregulated in a closed-loop mode via the volume flow of the other secondfuel such that the exhaust gases given off observe the preset emissionvalues. Therefore, it should be clear that “to control” should beunderstood as open-loop mode operation and “to regulate” should beunderstood as closed-loop mode operation.

There are various variants for the regulation according to theinvention. One which is preferred provides that the quantity of thesecond fuel supplied to the internal combustion engine per unit of timeis regulated by matching a mixture pressure influenced by it in anintake of the internal combustion engine to a mixture pressure targetvalue determined according to the output delivered and the presetnitrogen oxide emission value of the internal combustion engine. Thisrequires a measuring apparatus in the intake which determines thecurrent mixture pressure before the inlet valves. The actual value ofthe mixture pressure is matched to its target value by suitable settingof the quantity of the second fuel supplied per unit of time.

In another variant, however, instead of the mixture pressure, acorresponding λ-value in the exhaust gas can be measured. With thisvariant, it is provided that the quantity of the second fuel supplied tothe internal combustion engine per unit of time is regulated by matchinga λ-value influenced by it in an exhaust of the internal combustionengine to a λ-target value determined according to the output deliveredand the preset nitrogen oxide emission value of the internal combustionengine.

As is generally known, in this case the λ-value describes the proportionof air during combustion processes, λ=1 corresponding to astoichiometric combustion.

The method according to the invention is used particularly preferablywith, in particular stationary, gas engines, the first fuel being acombustible gas and/or the second fuel being a second combustible gas.Both the first and the second fuel can be mixtures for example ofvarious gases. It is also possible to add constituents or gases notcombustible per se to the first or second fuel, for example in order toburn these.

The method according to the invention can be used particularly favorablyif a change of the mixing ratio of the two fuels or a switch ofoperation of the internal combustion engine from operation with thefirst fuel to operation with the second fuel is proposed. In both cases,the method according to the invention makes it possible during the wholeswitch from one to the other fuel or during the whole change of themixing ratio to operate the internal combustion engine with presettablenitrogen oxide emission values. To this end, in a first operating modeon this side of a presettable operation-switching point the quantity ofthe first fuel supplied per unit of time is controlled or kept constantand the quantity of the second fuel supplied per unit of time isregulated, and in a second operating mode on the other side of thepresettable operation-switching point, the quantity of the second fuelsupplied per unit of time is controlled or kept constant and thequantity of the first fuel supplied per unit of time is regulated. Theoperation-switching point, can be defined via various parameters. Apresettable relationship between the quantity of the first fuel suppliedper unit of time and the quantity of the second fuel supplied per unitof time conveniently defines the operation-switching point.

BRIEF DESCRIPTION OF THE DRAWINGS

Further details and features of the present invention will be seen inthe following description of the figures, in which:

FIG. 1 Is a diagram illustrating the relationship known in the state ofthe art between the output P delivered by the internal combustion engineand the mixture pressure p₂ measured in the intake of the internalcombustion engine,

FIG. 2 Is a schematic view of an scheme according to the invention,

FIGS. 3 and 4 Are schematic view showing details of variations accordingto the invention of the design of a fuel-mixing apparatus,

FIGS. 5 and 6 Are diagrams illustrating the relationships of the outputP and the mixture pressure p₂ with the help of which the regulationmethod according to the invention is illustrated, and

FIG. 7 Is a diagram showing the pattern over time of the volume flowswhen switching from an operation with a first fuel type to operationwith a second fuel type.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows schematically the dependency known in the state of the artof the mixture pressure target value p₂ on the output P delivered by theinternal combustion engine when operating with one fuel type.Corresponding relationships between the λ-target value and the deliveredoutput P exist analogously and are therefore equally representable.However, because of the need for brevity, further explanation of themethod is given essentially with reference to the relationship betweenp₂ and P.

All those operating points of the internal combustion engine which eachhave a specific nitrogen oxide emission value lie on the shown solidcharacteristic line 10. The characteristic line or the characteristicsfield is created by gauging, for example when starting up the internalcombustion engine. This happens by setting a mixture pressure at anoperating point 9 with given output P such that the desired nitrogenoxide emission value of the internal combustion engine results. Thismixture pressure is then the mixture pressure target value p₂ at thegiven output P. In order to create a characteristic line 10, at least asecond operating point 9 is then started by correspondingly settinganother output value P, with the mixture pressure p₂ at which thedesired nitrogen oxide emission value is reached again being determined.At first approximation, the two thus-determined operating points 9result in a characteristic line 10′ (shown as a dotted line). This canbe linear or run with the help of known polynomials or the like as abent curve through the operating points 9. If more than two operatingpoints 9 are gauged with the named procedure at a constant nitrogenoxide emission value, a linear or curved pattern (characteristic line10) can also result from this.

In the case of internal combustion engines in which certain operatingparameters, such as for example the temperature t₂ of the fuel/airmixture or the ignition point ZZP or the quality of the supplied fuelcan alter greatly, it may also be advisable to also take account of theinfluence of there parameters. A characteristic line generally thenresults. FIG. 1 shows by way of example various dashed characteristiclines 10″ which result in the case of corresponding gauging of operatingpoints 9″ in each case at constant nitrogen oxide emission values ineach case and different temperature values t₂ in each case. When accountis taken of several influencing parameters, the overall result is then amultidimensional characteristics field. Alternatively, taking a singlecharacteristic line 10 as a basis, but also corresponding correctionvalues for the temperature of the fuel/air mixture t₂ or the ignitionpoint ZZP or the quality of the supplied fuel, further influencingparameters can be taken into account. In order to set limits to theoutlay when gauging the characteristics field according to the proceduredescribed above, estimates can also be applied if the influence of aspecific parameter is known.

FIG. 2 shows an engine diagram, reduced to essentials, with which themethod according to the invention can be carried out. Firstly thisshows, as is known per se, an output regulator in which a PID controller1 adjusts an output servocontrol 2 (for example a throttle valve or aninlet valve) in such a way that the output P delivered by the engine 5corresponds to the desired output target value P_(soll). According tothe invention, a regulation section is provided for the engine 5 withwhich, to reach constant nitrogen oxide emission values NO_(x), a fuelmixing device 3 for at least two fuels—as explained further below—iscontrolled on the one hand and regulated on the other. Version variantsaccording to the invention for the fuel mixing device 3 are representedin FIGS. 3 and 4. These are also explained further below. In FIG. 2itself, in a first variant, a pressure-measuring apparatus 4 is arrangedin the intake 7 arranged behind the fuel mixing device 3 of the engine5. This supplies the regulator 6 with a current measured value for themixture pressure before the valves. The variant in which, instead of themixture pressure, a λ-value is used for regulation is represented bybroken lines. This can then be measured in the exhaust by means of aλ-sensor 4′ customary in the trade. In this variant also, the measuredvalue is supplied to the regulator 6. In addition to the measured outputP and the measured mixture pressure or λ-value, other engine parameterscan be supplied to the regulator 6 according to the invention, such asfor example the temperature t₂ of the fuel mixture or the ignition pointZZP or the lower calorific value hu or the volume flow 'V, in order tothen be able to use the multi-dimensional characteristics fields orrelationships briefly represented with the help of FIG. 1. The regulator6 controls the fuel mixing device 3 according to the regulation processof the invention that is once again described in detail further below.

FIG. 3 shows a first embodiment according to the invention for the fuelmixing device 3. In this, two different fuel types A and B (preferablytwo different combustible gases) are supplied to a mixer 8 via settablevolume flow dosage valves 11. In this mixer, the two fuel types A and Bare then blended with air to produce a combustible gas mixture which isthen supplied to the engine 5. Although the shown mixing device 3 can ofcourse also be used to supply only fuel A or only fuel B to the engine5, the method according to the invention serves to operate the engine atleast part of the time with both fuels or switch the engine fromoperation with one fuel to operation with the other fuel, while stillalways reaching presettable nitrogen oxide emission values. According tothe invention, it is provided that the volume flow dosage valve of thefirst fuel type A is controlled or kept constant according to a controltarget value preset, while the volume flow dosage valve 11 and thus thevolume flow of the second fuel type B is regulated according to anengine parameter, or vice versa.

FIG. 4 shows a further variant of a fuel-mixing device 3 which can alsobe used for a regulation method according to the invention. Here, fuel Bis supplied direct to an adjustable mixer 12. This mixes fuel B with airL. This mixture is then supplied to a second mixer 8, where the secondfuel type A is also added. The quantity of A supplied per unit of timecan in turn be set via the volume flow dosage valve 11. Here, too,according to the invention the volume flow of the one fuel type can becontrolled while the volume flow of the other fuel type is regulated inorder to reach the presettable nitrogen oxide emission values.

It is explained with reference to FIG. 5 how the respective mixturepressure target value p.sub.2 for various output values P when operatingwith two different fuel types can now be determined according to theinvention. Firstly, characteristic lines 10 must be determinedseparately from each other for both fuel types, as explained withreference to FIG. 1. When gauging, the internal combustion engine asknown in the state of the art is operated in each case with only onefuel, which may also be a mixture or contain non-combustible admixtures.

FIG. 5 shows the determination of the mixture pressure target value 15,for the sake of clarity using only one characteristic line 10 for fuel Aand only one other characteristic line 10 for fuel B. In addition, onlytwo operating points 9 each have been gauged for both characteristiclines 10. All the operating points 13 and 14 between the gaugedoperating points 9 can be calculated from these via equations or filedas a characteristics field in a suitable memory of the regulator 6.Instead of a linear interpolation, bent curves as characteristic lines10 can also be the basis for the calculation of the mixture pressuretarget value P₂ 15. This calculation itself can be realized as aninterpolation. Basically it is always a momentary mixture pressuretarget value P₂ 15 which can either be calculated on the basis of thecurrent preset values or filed as a characteristics field.

A favorable variant provides that the calculation is based on thecorresponding target values 13 and 14 and a standardization factor x.This can be determined for example according to the calorific value orthe CH₄ content of the first fuel A or of the second fuel B or of avolume flow of a fuel mixture. The standardization factor x can stand inboth a linear and a non-linear relationship with the named parameters.Taking into account that the standardization factor x is standardized tovalues between 0 and 1, the following calculation rule results for themixture pressure target value p₂ in point 15 (=p₂ (15):p₂(15)=p₂(13)+(p₂−(14)−p₂(13))x

Here, p₂(13) and p₂ (14) are the respective mixture pressure targetvalues are preset with the help of the characteristic lines 10 for fueltype A and fuel type B. According to the thus-calculated mixturepressure target value p₂ (15), the corresponding volume flow dosagevalve 11 or the corresponding volume flow-controllable gas mixer 12 ofthe fuel A or B to be regulated is then operated, while the other volumeflow dosage valve 11 or the other volume flow-controllable gas mixer 12for the other fuel is kept constant or controlled according to fixedpreset values. The calculation, explained with reference to P₂ and P, ofthe target value 15 operates analogously in the case of a regulationwhich is based on the λ-value and the output P.

FIG. 6 shows a variant of the invention in which, when calculating themixture pressure target value p₂ (15) or the λ-target value,fluctuations in the quality of the second fuel B must be taken intoaccount, preferably via previously determined characteristics fields ormeasured values corresponding to correction factors. Thus, therefrequently are fluctuations in fuel quality, for example, when usingwaste gases as fuel. In the shown example in FIG. 6 this is the case forfuel B. Owing to corresponding quality fluctuations, the mixturepressure target values for this fuel type then no longer lie on acharacteristic line, but in the area between two characteristic lines10′ and 10″. The respective current target value 13 for gas type B mustthen be determined first, using characteristic lines 10′ and 10″ gaugedas usual, from the values 13′ and 13″. An analogous standardizationfunction to that used to determine p₂ (15) can be used for thiscalculation, the standardization factor x being replaced by anotherstandardization factor y. y can for its part be determined, for example,via the current calorific value or the current composition of the fueland depend on this in a linear or non-linear manner. If the mixturepressure target value p₂ (13) characteristic of the current quality ofthe fuel B is calculated, the mixture pressure target value p₂ (15)needed for the regulation can, as shown with reference to FIG. 5, becalculated from the mixture pressure target values p₂ (13) and p₂ (14)with the help of the standardization factor x.

In the example shown, the CH₄ content of fuel B fluctuates between 40%and 60%. The characteristic line 10′ represents the relationship betweenP and p₂ for fuel B with a CH₄ content of 40%, the characteristic line10″ represents the corresponding relationship in the case of a CH₄content of fuel B of 60%. If not only the quality of a fuel B but alsothat of the other fuel A fluctuates, corresponding characteristic linesA′ and A″ (not represented here) must be gauged in order tocorrespondingly calculate the mixture pressure target value p₂ (14) fromsame.

FIG. 7 shows the patterns over time of the volume flow 16 of fuel A andof the volume flow 17 of fuel B in the case of a switchover, selected byway of example, of the operation of the internal combustion engine fromoperation with the first fuel A to operation with the second fuel B. Theoperation-switchover point is reached at a preset ratio of the volumeflows V′A to V′B at time t₂. The ratios in the operation-switchoverpoint are favorably between 1:4 and 4:1 and particularly preferablybetween 1:2 and 2:1. At time's less than t₂ the volume flow of fuel A isregulated according to the mixture pressure target value p₂ (15), whilethe volume flow of fuel B is increased following a preset incline. Attime t₂ the switch into a second operating mode then takes place. Fromthis point in time on, the volume flow of fuel B is regulated accordingto the mixture pressure target value p₂ (15), while the volume flow offuel A is reduced following a preset incline.

The invention is not limited to the shown embodiments. Thus, the methodaccording to the invention can also be applied to the operation of aninternal combustion engine with more than two fuel types, by for examplecontrolling two fuel types according to fixed preset values, while athird fuel type is regulated. A major advantage of the method accordingto the invention is that even when there are changes in the mixing ratioof different fuels at any chosen point in time the reaching of thedesired NO_(x) emission values is assured. In the simplest case themethod according to the invention can already be carried out on thebasis of only two characteristic lines (as shown in FIG. 5), theremaining values can then be calculated online in each case or filed incorresponding characteristics fields. A precise regulation is therebypossible even with more complicated mixing systems, the fuel mixturesupplied to the engine being known at any time and correspondingly ableto be precisely taken into account in the regulation. When converting aninternal combustion engine operated by the method according to theinvention, exclusively known components, such as mixers and volume flowdosage valves, can be used.

1. A method of regulating an internal combustion engine in order toreach presettable nitrogen oxide emission values of the internalcombustion engine, comprising: supplying the internal combustion engineat least a portion of an operating time with a first fuel and at least aportion of the operating time with a second fuel; controlling a quantityof the first fuel supplied to the internal combustion engine per unit oftime according to one of a preset control target value or a constantvalue; and regulating a quantity of the second fuel supplied to theinternal combustion engine per unit of time by matching a mixturepressure influenced by the quantity of the second fuel in an intake ofthe internal combustion engine to a mixture pressure target valuedetermined according to a delivered output and a preset nitrogen oxideemission value of the internal combustion engine so as to reach thepreset nitrogen oxide emission value.
 2. The method of claim 1, whereinthe first fuel is a first combustible gas, and the second fuel is asecond combustible gas.
 3. The method of claim 1, wherein the mixturepressure target value determined according to the delivered output andthe preset nitrogen oxide emission value is further determined accordingto corresponding target values intended for an operation of the internalcombustion engine with the first fuel and for an operation of theinternal combustion engine with the second fuel and further according toa standardization factor x.
 4. The method of claim 3, wherein thestandardization factor x is determined according to the calorific valueor the CH₄ content of the first fuel or of the second fuel or of a fuelmixture.
 5. The method of claim 3, wherein the mixture pressure targetvalue is further determined by taking into account fluctuations in thecomposition of the first fuel or of the second fuel via previouslydetermined characteristics fields or by correction values andcorresponding measured values.
 6. A method of regulating an internalcombustion engine in order to reach presettable nitrogen oxide emissionvalues of the internal combustion engine, comprising: supplying theinternal combustion engine at least a portion of an operating time witha first fuel and at least a portion of the operating time with a secondfuel; controlling a quantity of the first fuel supplied to the internalcombustion engine per unit of time according to one of a preset controltarget value or a constant value; and regulating the quantity of thesecond fuel supplied to the internal combustion engine per unit of timeby matching a λ-value influenced by the quantity of the second fuel inan exhaust of the internal combustion engine to a λ-target valuedetermined according to a delivered output and a preset nitrogen oxideemission value of the internal combustion engine so as to reach thepreset nitrogen oxide emission value.
 7. The method of claim 6, whereinthe first fuel is a first combustible gas, and the second fuel is asecond combustible gas.
 8. The method of claim 6, wherein the λ-targetvalue determined according to the delivered output and the presetnitrogen oxide emission value is further determined according tocorresponding target values intended for an operation of the internalcombustion engine with the first fuel and for an operation of theinternal combustion engine with the second fuel and further according toa standardization factor x.
 9. The method of claim 8, wherein thestandardization factor x is determined according to the calorific valueor the CH₄ content of the first fuel or of the second fuel or of a fuelmixture.
 10. The method of claim 8, wherein the λ-target value isfurther determined by taking into account fluctuations in thecomposition of the first fuel or of the second fuel via previouslydetermined characteristics fields or by correction values andcorresponding measured values.
 11. A method of regulating an internalcombustion engine in order to reach presettable nitrogen oxide emissionvalues of the internal combustion engine, comprising: supplying theinternal combustion engine at least a portion of an operating time witha first fuel and at least a portion of the operating time with a secondfuel; performing a first operating mode at a first side of a presetoperation-switching point, the first operating mode including:controlling a quantity of the first fuel supplied to the internalcombustion engine per unit of time according to one of a preset controltarget value or a constant value; and regulating the quantity of thesecond fuel supplied to the internal combustion engine per unit of timeaccording to at least one recorded engine parameter so as to reach thepreset nitrogen oxide emission value; performing a second operating modeat a second side of the preset operation-switching point, the secondoperating mode including: controlling a quantity of the second fuelsupplied to the internal combustion engine per unit of time according toone of a preset control target value or a constant value; and regulatingthe quantity of the first fuel supplied to the internal combustionengine per unit of time according to at least one recorded engineparameter so as to reach the preset nitrogen oxide emission value; andswitching an operating mode of the internal combustion engine betweenthe first operating mode and the second operating mode.
 12. The methodof claim 11, wherein the first fuel is a first combustible gas, and thesecond fuel is a second combustible.
 13. The method of claim 11, whereinsaid switching comprises switching an operating mode of the internalcombustion engine so as to change a mixing ratio between the first fueland the second fuel whereby both the first fuel and the second fuel aresupplied to the internal combustion engine.
 14. The method of claim 11,wherein said switching comprises switching an operating mode of theinternal combustion engine such that an operation using one of the firstfuel and the second fuel is replaced by an operation using the other ofthe first fuel and the second fuel.
 15. The method of claim 11, whereinthe preset operation-switching point is defined by a preset ratiobetween the quantity of the first fuel supplied per unit of time and thequantity of the second fuel supplied per unit of time.
 16. The method ofclaim 15, wherein the preset ratio of the operation-switching point isbetween 1:4 and 4:1.
 17. The method of claim 15, wherein the presetratio of the operation-switching point is between 1:2 and 2:1.
 18. Aregulation section for use with an internal combustion engine, saidregulation section comprising: a fuel mixing device; and a regulatoroperable to control said fuel mixing device to: supply the internalcombustion engine at least a portion of an operating time with a firstfuel and at least a portion of the operating time with a second fuel;control a quantity of the first fuel supplied to the internal combustionengine per unit of time according to one of a preset control targetvalue or a constant value; and regulate a quantity of the second fuelsupplied to the internal combustion engine per unit of time by matchinga mixture pressure influenced by the quantity of the second fuel in anintake of the internal combustion engine to a mixture pressure targetvalue determined according to a delivered output and a preset nitrogenoxide emission value of the internal combustion engine so as to reachthe preset nitrogen oxide emission value.
 19. The regulation section ofclaim 18, wherein said fuel mixing device includes: a first volume flowdosage valve for supplying the first fuel to the internal combustionengine; and a second volume flow dosage valve for supplying the secondfuel to the internal combustion engine.
 20. The regulation section ofclaim 18, wherein said fuel mixing device includes: a volume flow dosagevalve for supplying the first fuel to the internal combustion engine;and a volume flow-controllable gas mixer for receiving the second fueland supplying the second fuel to the internal combustion engine.
 21. Aregulation section for use with an internal combustion engine, saidregulation section comprising: a fuel mixing device; and a regulatoroperable to control said fuel mixing device to: supply the internalcombustion engine at least a portion of an operating time with a firstfuel and at least a portion of the operating time with a second fuel;control a quantity of the first fuel supplied to the internal combustionengine per unit of time according to one of a preset control targetvalue or a constant value; and regulate the quantity of the second fuelsupplied to the internal combustion engine per unit of time by matchinga λ-value influenced by the quantity of the second fuel in an exhaust ofthe internal combustion engine to a λ-target value determined accordingto a delivered output and a preset nitrogen oxide emission value of theinternal combustion engine so as to reach the preset nitrogen oxideemission value.
 22. The regulation section of claim 21, wherein saidfuel mixing device includes: a first volume flow dosage valve forsupplying the first fuel to the internal combustion engine; and a secondvolume flow dosage valve for supplying the second fuel to the internalcombustion engine.
 23. The regulation section of claim 21, wherein saidfuel mixing device includes: a volume flow dosage valve for supplyingthe first fuel to the internal combustion engine; and a volumeflow-controllable gas mixer for receiving the second fuel and supplyingthe second fuel to the internal combustion engine.
 24. A regulationsection for use with an internal combustion engine, said regulationsection comprising: a fuel mixing device; and a regulator operable tocontrol said fuel mixing device to: supply the internal combustionengine at least a portion of an operating time with a first fuel and atleast a portion of the operating time with a second fuel; perform afirst operating mode at a first side of a preset operation-switchingpoint, the first operating mode including: controlling a quantity of thefirst fuel supplied to the internal combustion engine per unit of timeaccording to one of a preset control target value or a constant value;and regulating the quantity of the second fuel supplied to the internalcombustion engine per unit of time according to at least one recordedengine parameter so as to reach the preset nitrogen oxide emissionvalue; perform a second operating mode at a second side of the presetoperation-switching point, the second operating mode including:controlling a quantity of the second fuel supplied to the internalcombustion engine per unit of time according to one of a preset controltarget value or a constant value; and regulating the quantity of thefirst fuel supplied to the internal combustion engine per unit of timeaccording to at least one recorded engine parameter so as to reach thepreset nitrogen oxide emission value; and switch an operating mode ofthe internal combustion engine between the first operating mode and thesecond operating mode.
 25. The regulation section of claim 24, whereinsaid fuel mixing device includes: a first volume flow dosage valve forsupplying the first fuel to the internal combustion engine; and a secondvolume flow dosage valve for supplying the second fuel to the internalcombustion engine.
 26. The regulation section of claim 24, wherein saidfuel mixing device includes: a volume flow dosage valve for supplyingthe first fuel to the internal combustion engine; and a volumeflow-controllable gas mixer for receiving the second fuel and supplyingthe second fuel to the internal combustion engine.